Switched-Mode Power Supplies (SMPS) are being increasingly used in many domestic and industrial applications. In applications such as televisions or computer monitors, the application may require a number of states or modes of operation. A first `off` mode occurs when there is no power supplied to a device (or when a master switch is off); a second `on` mode occurs when the device is switched to an operating normally; and a third mode (referred to as a standby mode) occurs when the device is to remain powered, but with reduced functions and reduced power consumption. A standby mode may be encountered in a television via an `off` switch of a remote control, which typically does not switch the television fully off, but allows certain circuitry within the television to remain powered, so that if the `on` button of the remote control is pressed, the television will return to the `on` mode.
There is a need to reduce the power consumed by the SMPS during standby mode, so that use of mains electricity is reduced. At present there is a goal to reduce the power consumption during standby mode to a value of the order of 1 Watt.
Burst mode SPMS are known, which have an efficient power consumption in standby mode. However the PWM control apparatus are not easy to implement for burst-mode SMPS, they generate much noise due to the `burst` nature of their operation, and they require a large number of connections and external components, leading to a semiconductor package having many connection pins, and a large printed circuit board with many components.
Therefore what is needed is PWM control apparatus for SMPS with a reduced number of discrete components, a reduced pin count and size, and low power consumption in standby mode.
This invention seeks to provide a power supply which mitigates the above mentioned disadvantages.